Field of the Invention
The present invention relates to a technology of an X-ray photography.
Description of the Background Art
Conventionally, CT scan (Computed Tomography) is performed using an X-ray photography apparatus for the purpose of a medical diagnosis or a non-destructive inspection. In the X-ray photography apparatus, multi energy scan that photographs an identical region of an object is performed with plural X-rays having different X-ray energy distributions (for example, see Japanese Patent Application Laid-Open No. 2008-54831).
In the multi energy scan, tomographic images corresponding to the X-rays having different energy distribution characteristics can be obtained with respect to an identical sectional surface in the identical region of the object. For example, an image of a specific region can be extracted by obtaining a difference between the tomographic images having the different energy distribution characteristics.
In an X-ray CT photography apparatus described in Japanese Patent Application Laid-Open No. 2008-54831, a subject is disposed between an X-ray tube of a radiation source and an X-ray detector of detection means for detecting a radiation. At this point, the X-ray tube and the X-ray detector are rotated by 360 degrees about a rotation axis set to a center of a CT scan area. Two kinds of filters are arrayed between the X-ray tube and the subject in order to vary the energy distribution of the transmitted X-ray each other. For this reason, the subject is simultaneously radiated from the right and left with the X-rays having the different energy distributions.
In a helical scan type X-ray CT apparatus, two detectors having different energy characteristics are continuously disposed in a slice direction to perform dual energy scan (for example, see Japanese Patent Application Laid-Open No. 6-296607 (1994)).
However, for the X-ray CT photography apparatus described in Japanese Patent Application Laid-Open No. 2008-54831, the X-ray is scattered in a boundary portion between the two kinds of filters. Because of a considerable distance from the two kinds of filters to the X-ray detector, the scattered X-ray is incident on a position distant from a position on which the X-ray should originally be incident. Therefore, there is a risk of blurring the obtained projection image.
In Japanese Patent Application Laid-Open No. 6-296607 (1994), the two detectors include two scintillators having different thicknesses or two filters in which at least X-ray absorptances, thicknesses, shapes, or materials differ from each other, thereby varying the energy characteristic. Therefore, the X-ray scattered in the boundary portion between the two filters or the two scintillators is intensively incident on a specific position of each detector. Therefore, there is a risk of hardly detecting the X-ray, which is transmitted through the photographing area where the X ray should originally be detected, at the scattered X-ray incident position of the detector.